Such apparatus for mounting semiconductor chips is known in the trade as Die Bonder. The apparatus serves to mount the numerous uniform chips of a wafer that are located next to each other on a chip carrier one after the other onto a substrate, eg, a metallic leadframe. The Die Bonder comprises a wafer table on which the chip carrier is located, a transport system for delivering the substrates and a Pick and Place system to remove the semiconductor chips from the chip carrier and to place them onto the substrate. The Pick and Place system comprises a bondhead with a chip gripper that is moved back and forth by a drive system. The chip gripper can be rotated on a vertical axis so that the rotary position of the semiconductor chip can be altered if necessary. The chip gripper contains an exchangeable gripper that is a suction organ to which vacuum can be applied that is known in the trade as a “pick up tool” or “die collet”.
Extremely high demands are placed on an apparatus of this type. For the further processing of the mounted chips, they have to be accurately positioned onto the substrate. It is therefore necessary that the position of the rotational axis of the chip gripper and the position of the gripper axis of the chip gripper are known with great accuracy. In the ideal case, the rotational axis and the gripper axis coincide. Today, various methods are applied to determine the position of the rotational axis and the position of the gripper axis of the chip gripper:    a) The chip gripper is equipped with a metallic tip instead of the suction organ. The chip gripper is brought into different rotary positions and in each rotary position an imprint of the metallic tip is produced on a soft metal. From the position of the imprints produced, the eccentricity of the metallic tip is determined in relation to the rotational axis. This method has the disadvantage that the metal tip can have a different centre to that of the suction organ used afterwards in production.    b) The chip gripper is brought into different rotary positions and in each rotary position, an imprint of the suction organ is produced on a Teflon tape. From the position of the imprints produced, the eccentricity of the gripper axis of the suction organ is determined in relation to the rotational axis. A disadvantage with this method is that the imprints are often hardly recognisable so that the evaluation can not be done without the aid of an operator.    c) The suction organ is purposefully contaminated and an imprint is produced on a semiconductor chip that is to be picked. A disadvantage here is that the contamination leaves a residue on the semiconductor chip that can lead to problems with the subsequent wiring of the semiconductor chip by means of a Wire Bonder.